Shares of King Digital Entertainment Plc, maker of the wildly popular “Candy Crush Saga” game, fell as much as 15 percent in their trading debut on Wednesday, underscoring concerns about the company’s reliance on a single hit game.

King’s shares fell to a low of $19.08 from their IPO price of $22.50, valuing the company at about $6 billion.

“With King Digital, there is a lot of concern about its ability to keep coming up with popular games,” said Jay Ritter, a professor and IPO expert at the University of Florida.

“The offer price was set at the middle of the filed price range, indicating that there was neither exceptionally strong nor exceptionally weak demand,” Ritter said.

The two-year-old Candy Crush game, in which users move candies to line up at least three in the same color, has a seemingly endless supply of new levels and features to keep its nearly 100 million users occupied every day.

Its success has spawned reports of Candy Crush addiction with a Facebook page dedicated to addicts of the game, in which users get daily bonuses and new levels every few weeks.

The free game has been downloaded more than 500 million times since its launch on mobile devices. Using the “freemium” model, King makes money by selling players extra lives, lucky candy and other add-ons.

King sold 15.5 million shares of the 22.2 million offered, with the rest coming from stakeholders including private equity firm Apax Partners, which remains the biggest shareholder. London-based King raised about $500 million in its IPO.

In February, King said an average 144 million daily active users played its games more than 1.4 billion times per day.

King’s IPO is the largest by a mobile gaming company since Zynga Inc. went public in 2011, valuing the maker of “Farmville” at $7 billion.

Zynga’s market value has since shrunk to just over $4 billion, another victim of concerns about the danger of investing in companies that rely heavily on a hit game.

Zynga’s shares fell 4 percent.

While King also offers about other 180 games, about three-quarters of its revenue comes from “Candy Crush.”

“We’re building on traffic from ‘Candy Crush,’” Chief Executive Riccardo Zacconi said in an interview on CNBC, adding that the users attracted by the game will play its other games.

Zacconi rejected suggestions that his company faced the same issues as Zynga, which was heavily dependent on Facebook.

“I think we’re different because we cracked mobile, not only reach, but monetization, which allows us to buy marketing and be in control of the steering wheel … we are not reliant on someone featuring us,” he said.

JPMorgan, Credit Suisse and BofA Merrill Lynch were lead underwriters for the offering.

King, formerly known as King.com, was saved from bankruptcy by a last-minute infusion of capital on Christmas Eve 2003. It finally turned a profit in 2005 and has made money ever since.

“Candy Crush,” which was first launched on Facebook in April 2012, was released on Apple devices in November that year, followed by a launch on Android devices a month later.

The spectacular popularity of “Candy Crush” helped King generate revenue of $602 million in the fourth quarter of 2013 — up from $22 million in the first quarter of 2012.

The company says 1 trillion candies have been crushed so far and users have racked up 103,000 years of play time. Two-thirds of players are women.

The stock’s less-than-impressive debut will be noted by youthful rivals such as San Francisco-based Kabam and Kixeye — known for strategy games like “Kingdoms of Camelot” and “War Commander” — which are expected to seek market listings or new financing.

However, unlike most other tech companies that have gone public recently, King is profitable, has no debt and generated positive cash flow from operations for each of the last nine years. It posted profit before tax of $714.3 million in 2013.

Apax will retain a 44.2 percent stake in the company, if underwriters fully exercise their option to buy shares.

Zacconi, who has led King since co-founding the company in Sweden in 2003, will hold a 9.5 percent stake.